blob: 8ee05e1d20384baccfc1e14d2f5b64e5ee78b635 (
plain) (
blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
|
/*
* Copyright © 2009 Keith Packard <keithp@keithp.com>
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; version 2 of the License.
*
* This program is distributed in the hope that it will be useful, but
* WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* General Public License for more details.
*
* You should have received a copy of the GNU General Public License along
* with this program; if not, write to the Free Software Foundation, Inc.,
* 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA.
*/
#include "aoview.h"
static int16_t altitude_table[] = {
#include "altitude.h"
};
#define ALT_FRAC_SCALE (1 << ALT_FRAC_BITS)
#define ALT_FRAC_MASK (ALT_FRAC_SCALE - 1)
int16_t
aoview_pres_to_altitude(int16_t pres)
{
uint8_t o;
int16_t part;
if (pres < 0)
pres = 0;
o = pres >> ALT_FRAC_BITS;
part = pres & ALT_FRAC_MASK;
return ((int32_t) altitude_table[o] * (ALT_FRAC_SCALE - part) +
(int32_t) altitude_table[o+1] * part + (ALT_FRAC_SCALE >> 1)) >> ALT_FRAC_BITS;
}
int16_t
aoview_altitude_to_pres(int16_t alt)
{
int16_t span, sub_span;
uint8_t l, h, m;
int32_t pres;
l = 0;
h = NALT - 1;
while ((h - l) != 1) {
m = (l + h) >> 1;
if (altitude_table[m] < alt)
h = m;
else
l = m;
}
span = altitude_table[l] - altitude_table[h];
sub_span = altitude_table[l] - alt;
pres = ((((int32_t) l * (span - sub_span) + (int32_t) h * sub_span) << ALT_FRAC_BITS) + (span >> 1)) / span;
if (pres > 32767)
pres = 32767;
if (pres < 0)
pres = 0;
return (int16_t) pres;
}
|
